There are two kinds of main systems for endo-osseous dental implants which are commonly used today.
One system utilizes fixtures provided with threads which are threaded into a hole drilled into the jaw-bone. This system can be exemplified by the so-called Br.ang.nemark system.TM.. This system comprises both threaded fixtures which are to be screwed into holes which have been provided with threads in advance and self-tapping fixtures which are screwed into a non-pretapped hole drilled in the jaw-bone.
The other system commonly used can be exemplified by the so called IMZ-implant, which utilizes a cylinder provided with a rough surface serving as a fixture and which gently is tapped into a bore-hole in the jaw-bone. The roughness of the surface has no specific orientation.
The threaded fixtures have some important advantages, a major one being a result of the fact that the main loads in the clinical situation are axial loads. Threaded implants are very well suited to support axial loads and this may be particularly important in the initial stages of the osseointegration process in which it is important that the implant is fully stable and as immovable as possible in the bore-hole. The term "osseo-integration" as coined by Prof Br.ang.nemark and his coworkers in Gothenburg during the seventies and as used here refers to the close apposition between bone tissue and implants that for instance may be obtained by using implants made of titanium.
There are however some inherent disadvantages in this construction, one of the major ones being the time and the care needed to screw a self-tapping implant into a hole. If the hole also has to be provided with threads in advance, the total period of time needed for the operation of course will be much greater. Although a conventional threaded implant conceivably could be tapped into a hole having almost the same diameter as the major diameter of the threads, the distance the bone tissue would have to grow into the threads would be excessive and the time needed for the osseo-integration process would be long.
The rough-surfaced cylindrical implant is very simple to insert and the time needed for this is short. It may however happen that implants having this design gets stuck in the bore-hole before the implant is fully inserted, which may result in an unacceptable trauma to the bone tissue, both if the implant is inserted entirely by force and if the implant is extracted by force. Both the initial and the final stability of the implant will be less than the initial and the final stability of a threaded implant.